1. Field of the Invention
The present invention relates to an intermediate hopper and an image forming apparatus. More particularly, the present invention relates to an intermediate hopper for temporarily containing toner to be supplied to a developing device and an image forming apparatus such as an electrostatic copying machine, a laser printer and a facsimile machine that forms images by an electrophotographic method by guiding the toner contained in the intermediate hopper to the developing device.
2. Description of the Related Art
In the image forming apparatus using the electrophotographic method, an electrostatic latent image is formed on a surface of a photoconductor drum (toner image holder), toner is supplied to the photoconductor drum by means of a developing device to develop the electrostatic latent image, a toner image formed on the photoconductor drum through the development is transferred onto a sheet such as a paper sheet, and the toner image is fixed onto the sheet by means of a fixing device.
Since the toner is consumed at every image formation, the developing device is replenished with toner stored in a toner cartridge. Nowadays, there is an image forming apparatus available which employs an intermediate hopper for temporarily containing toner instead of supplying the toner directly from a toner cartridge to a developing device.
In this image forming apparatus, the toner stored in the toner cartridge is supplied to the intermediate hopper, and the toner supplied to the intermediate hopper is supplied to the developing device.
The intermediate hopper includes a toner reception tub for containing a toner, and the toner reception tub is provided with a toner amount detection sensor for checking presence or absence of the toner supplied to the intermediate hopper.
With such an intermediate hopper, even when the toner in the cartridge runs out, it is possible to secure the time needed to remove the empty toner cartridge and replace it with a new toner cartridge without suspending a printing operation in the image forming apparatus, because the intermediate hopper contains the toner.
That is, with the intermediate hopper, it is possible to continue an image formation operation during the replacement of the toner cartridge (referred to as continuous run).
For example, Japanese Unexamined Patent Application Publication No. 2009-251169 proposes an intermediate toner hopper comprising: a container tank for temporarily containing toner discharged from a toner bottle; and two carrying screws arranged in the container tank so that axis lines thereof are parallel to each other for carrying the toner in opposite directions by rotating in opposite directions, wherein the toner discharged from the toner bottle is received through a toner supply opening formed in the container tank and temporarily contained, guided toward a toner discharge opening formed in the container tank while being circulated and carried by the rotation of the two carrying screws, and then discharged into a developing device through the toner discharge opening (see FIGS. 1 and 4, and paragraphs 0056 to 0067).
While being able to discharge some of the toner being circulated and carried inside the container tank swiftly by using the two carrying screws, the conventional intermediate toner hopper as described above is disadvantageous in that the toner stays at an end of the container tank, because the two carrying screws do not have a partition therebetween.
In addition, when the toner is carried under agitation by the carrying screws and the flowability of the toner is decreased for some reason, there may be generated a region having a locally decreased toner density. In this case, the above-mentioned toner amount detection sensor for detecting presence or absence of the toner may detect such a region having a decreased toner density to falsely conclude that no toner is remaining.
As a result, despite the fact that the toner is remaining in the intermediate toner hopper, toner will be supplied from a toner supplying device to a toner receiving port of the intermediate toner hopper based on the conclusion that no toner is remaining, and therefore the toner gets stuck at the toner receiving port of the intermediate toner hopper (referred to as toner bridging).
Due to the toner bridging, disadvantageously, the toner cannot be supplied to the developing device, prevented from being carried normally in the intermediate toner hopper.
In addition, if supply of toner from the toner bottle is suspended for replacement of the toner bottle while the toner is circulated and carried in the intermediate toner hopper, the toner carrying paths will have a region having no toner or a region having a low toner density (hereinafter, referred to as toner-missing space).
The toner-missing space is also carried toward the toner discharge opening with the toner carried by the carrying screws. When the toner-missing space reaches the toner discharge opening, the supply of the toner to the developing device is suspended to reduce the toner density in the developing device. The toner thus supplied unsteadily and nonuniformly may cause an uneven image.